1. Field of the Invention
The invention relates to a fairing arrangement for an aircraft and is primarily concerned with a fairing arrangement for a control surface such as an aileron for a wing of the aircraft.
2. Discussion of Prior Art
Control surfaces of aircraft are frequently operated by means of actuator jacks. The size of the actuator and the geometry of the wing and control surface often lead to the actuator protruding below the lower surface of the wing and a fairing arrangement is required to cover the jack or other actuating device. The present invention is primarily concerned with a fairing arrangement of that kind.
Various prior fairing arrangements involving flexible seals between a first fairing portion on a fixed structure such as a wing and second fairing structure on a control surface are described in GB-A-2323576. The seals maintain an aerodynamic profile and help to prevent ingress of debris etc. The seals disclosed are intended to operate over the full range of control surface movement or at least a major part of such movement and the seals need to be fairly long in the fore and aft direction. Long flexible seals are not ideal from the point of view of maintaining aerodynamic shape. Moreover, the deflection which is experienced makes the seals prone to fatigue and hence they have a short life in service which, again, is not ideal. Also, such long seals tend to experience a substantial amount of deflection particularly when the control surface is at an extremity of movement, for example where the ailerons droop to, say, xe2x88x9230xc2x0 from a straight and level flight position when the aircraft is standing idle. Prior art seals have all been generally spherical in shape and this has tended to force a foreshortening of the overall fairing shape upon the designer in an attempt to avoid discontinuity of shape where the seal is encountered. This is not ideal, aerodynamically. In addition to the different aerodynamic shape which the, usually elongate, seal imposes on the fairing, all known prior art designs of seal have protruded into the airstream proud of the fairing, in cruise. Again this is undesirable, aerodynamically, owing to induced drag.
Normally, the fairings extend in the direction of flight whereas the usual hinge axis of the aileron lies at an angle, e.g. around 60xc2x0 to the direction of flight. Therefore, in addition to the seals being able to accommodate at least a major part of the range of movement of the control surface, such seals also need to cope with translational movement of the ailerons which occurs as a result of the hinge axis being arranged at an angle to the direction of flight.
An object of the present invention is to provide an improved fairing arrangement for an aircraft which reduces or eliminates the problems outlined above yet enables sealing to be effective over the normal operational range of movement of the control surface.
According to one aspect of the invention there is provided a fairing arrangement for an aircraft comprising a first fairing portion on a fixed structure such as a wing and a second fairing portion on a control surface mounted on the fixed structure, the fairing arrangement protruding outwardly of the aerodynamic profile of the fixed structure and the control surface being angularly displaceable with respect to the fixed structure through a range of movement of the control surface between positive and negative limits either side of a straight and level flight position, parts of the first and second fairing portions being arranged so as to overlap each other over a normal operational range of the control surface to form a seal and being arranged so as not to form a seal over the remainder of the range in one of the directions of movement of the control surface.
By providing a seal which is effective primarily over the normal operational range of the aileron, the service life of the seal can be extended.
The fairing arrangement preferably extends in the direction of flight of the aircraft, i.e. the fore-and-aft direction, whereas the control surface may be angularly displaceable about a hinge line inclined at an angle to the direction of flight. In such a case, the seal may be of S-shaped form in order to maintain a seal during movement of the control surface about the inclined hinge line.
Preferably, the overlap parts form a seal over the entire remainder of the range of movement of the control surface in the other of the directions of movement from the straight and level flight position.
The remainder of the range is preferably in the negative direction of angular movement of the control surface.
One of the overlap parts may form a sealing surface for co-operation with the other overlap part. Preferably, said one of the overlap parts defines an oblique sealing surface which extends substantially in the direction of a path of movement of the control surface over the normal operational range of movement of the control surface. Preferably, said one overlap part is tapered towards the other to form the oblique surface.
By arranging for one of said overlap parts to provide a sealing surface which extends substantially in the direction of the path of movement of the control surface, any significant deflection of one or both overlap parts, usually in a direction normal to the direction of control surface movement, during movement of the control surface over the normal operating range can be minimised if not avoided altogether which is of considerable advantage from the point of view of durability. Moreover, as the sealing surface does not have to seal outside the normal operational range of control surface movement in one direction of movement, it can be made smaller in the fore-and-aft direction which is helpful at least from the point of view of maintaining aerodynamic shape
Preferably, the overlap parts overlap slightly at one end of the operational range of movement of the control surface and/or overlap substantially fully at the other end of the operational range.
The sealing surface preferably extends in the fore-and-aft direction so as to be effective to seal over substantially its whole fore and aft extent.
In a preferred embodiment, one of the overlap parts comprises a sealing element which is preferably flexible and made, for example, from a fabric, rubberised or plastics material. The use of a flexible sealing element is useful in that it can effectively take up tolerances between the overlap parts to minimise or eliminate any gap therebetween. The sealing element may make contact with the other overlap part at least over part of the normal operational range of movement of the control surface. Preferably, the sealing element provides the said sealing surface.
A said overlap part may be formed with a lead-in portion to ensure correct co-operation with the other overlap part. The lead in portion is preferably curved.
Preferably, the sealing element is mounted on its associated fairing portion via a joint which minimises discontinuity between the outer surface of the fairing portion and the sealing element. The joint may be a halving-type joint. Conveniently, the sealing element may be carried by the first fairing portion.
In a preferred embodiment, the overlap part of the other fairing portion tapers towards said one overlap part to define a further oblique surface which provides a second sealing surface. The overlap part providing the further oblique surface may be tapered to form that surface. The said second sealing surface may also lie substantially in the direction of the path of movement of the control surface over the normal operational range of movement of the control surface. Preferably, the first and second sealing surfaces lie closely adjacent or in contact with each other throughout the normal operational range of movement of the control surface. Where the surfaces are in contact with each other, the first and second surfaces may slide across each other during movement of the control surface throughout the normal operational range.
The normal operating range of movement may be up to xc2x15xc2x0
The first and/or second sealing surface is preferably elongate in a direction transverse to the fore-and-aft direction. In such a case, the first and/or second sealing surface may be substantially S-shaped in its longitudinal direction and may be generally arcuate to accommodate the movement of the control surface about the inclined a hinge line.
Preferably, the angle of taper varies over the length of the sealing surface. Such an arrangement further helps to maintain the seal where movement of the control surface takes place about a hinge line arranged at an angle to the direction of flight.
According to another aspect of the invention there is provided an aircraft flying surface having a fairing arrangement thereon according to the first aspect of the invention or any of the consistory clauses relating thereto.
According to a further aspect of the invention there is provided an aircraft having thereon a fairing arrangement according to the first aspect of the invention or any of the consistory clauses relating thereto.
A fairing arrangement in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: